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I fitted a Denali Sounbomb Mini, as it was listed as plug and play on a 1090, so no relay required.
Wrong, it would give a General Error message as soon as you hit the horn button.
So I fitted a relay, and thought my problems would be over. A couple of quick test beeps and all was fine.

Out on the road however, when I needed to use it for a longer blast, it again triggered a General Error warning. Having tested it this happens even with the horn disconnected from the relay. Is the problem now that the relay is seen as too low a load by the Canbus system, so should I add a resistor in to the relay circuit?
 

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All you need to do is keep the original horn in place and connected... then wire the relay 85 and 86 terminals in parallel with the original horn.... the power for the new horn comes from battery to terminals 87 and 30......this way the ecu knows the horn current is fine and dosnt notice the relay winding current so no fault showing
 

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Discussion Starter #5
All you need to do is keep the original horn in place and connected... then wire the relay 85 and 86 terminals in parallel with the original horn.... the power for the new horn comes from battery to terminals 87 and 30......this way the ecu knows the horn current is fine and dosnt notice the relay winding current so no fault showing
Yes, that would work, except I've mounted the new horn in place of the original, so it will be easier to fit a resistor in circuit.
 

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Is there an obvious mains feed for the relay in the headlamp housing?
You could use the Pos form acc1 but I think the wire is a bit thin and would be under a bit of pressure to work the add on horn properly ...running it off the battery pos makes sure it all works proper
 

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Ok thanks for the reply. Understand keeping the original horn as a resistor to stop the dash error, dont like running wires up and down the bike so would have prefered a feed from the something in the can of worms but easier from the battery. Thanks again.
 

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I have found with the fooking can-bus ecu shite.....Run two decent wires from battery to a small fuse block, use ignition Acc to operate a 40amp relay then just wire every extra to that. Run the ground through the horn switch circuit, Ecu will just think you've never used horn......no need to install resistors that just get hot and pop etc and throw old horn in scrap bin.
 

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Run the ground through the horn switch circuit, Ecu will just think you've never used horn......no need to install resistors that just get hot and pop etc and throw old horn in scrap bin.
That's very brave of you.
I've just been umming and ahhing over how safe it is to do that and have come to the conclusion that it's probably fine. :)
The ECU is probably going to see the full 14 volts from the current shunt when running (& with the horn not activated), so by doing what you've suggested it will just never know the horn isn't there.

So... neat tip - thank you.
 

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That's very brave of you.
I've just been umming and ahhing over how safe it is to do that and have come to the conclusion that it's probably fine. :)
The ECU is probably going to see the full 14 volts from the current shunt when running (& with the horn not activated), so by doing what you've suggested it will just never know the horn isn't there.

So... neat tip - thank you.
Ive read that twice and I don't follow. The horn circuit is always open (no horn) until you hit button, running earth through handle bar switch...if there is a short on return wire horn will sound and no blown fuses, short on feed no horn and no blown fuses. I do this because the bars are one of those places where grip/switches move in an off.
 

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The horn switches on motorcycles are in effect a pull down switch system. The horn has a live feed and the switch makes the circuit by providing the negative connection.

The ECU is obviously monitoring this and there are 2 ways it can do it. It can have a current shunt (low value resistor) in the feed circuit and sense the current taken when in use or it can pass a low current through the item all the time (as it does with bulbs).
It seems they've gone for the first option so the ECU will be looking for 2 possible valid conditions.
12 - 14 volts is normal for the horn not being used. Then there will a lower voltage for when being used, lets say 1 to 2 volts at the shunt. So if a different voltage appears (like what would happen with just a relay coil in circuit instead of the horn) when the button is pressed, the ECU will assume the horn has failed. This also means that if the horn is disconnected, pressing the button shouldn't trigger an error either.

Initially when I read your post I thought.. "hang on, this could be feeding 12 volts back up the bikes wiring to the ECU", which is exactly what it is doing. Then after some pondering I have come to the conclusion that this already happens anyway, because the only practical way to monitor current flow is via a shunt resistor, and if the shunt resistor is on positive side of the circuit then it will go to full voltage whenever the horn switch is open.

Does that make it clearer?
If not then it's white board and dry markers I'm afraid.:)
 

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So the assumption is that the horn switch goes to earth when operated like in the old days.........it more than likely puts out a can bus signal to ecu to tell it to operate the horn....I might be wrong but assumption is the mother of all fuck ups
 

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So the assumption is that the horn switch goes to earth when operated like in the old days.........it more than likely puts out a can bus signal to ecu to tell it to operate the horn....I might be wrong but assumption is the mother of all fuck ups
Yes, you're right.
I decided to open up the manual for my 1190 and actually look at the wiring diagrams.
If this is true (and it looks like it is) then wiring up the relay through that switch wouldn't be a good idea.

I can't see if that whole switch cluster is wired to be common high or low, I suspect low.
If so it would operate the relay and work but I don't think KTM switches are very good. I think they are only rated for very small signal currents, a relay coil might cause damage to them.

EDIT: Just looked through the manual for my older 990 and sure enough it is shown as being wired directly to the horn switch. So I think we can assume that on the newer 'CAN bus' bikes the horn switch does not directly operate the horn, rather it signals a controller to do it. Therefore I personally would not interfere with the bikes in the way described. I would however fit the load resistor as shown in the video because that is simply reproducing the effect of having a functional horn fitted.
 
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